So, running on 2.5.5 I would do the following (with SafeCracker instead):
{exp:channel:form channel="resumeer" return="folketinget/resume_ret/ENTRY_ID" include_jquery="no"}
Overskrift: <input type="text" name="title" id="title" value="{title}" size="50" maxlength="100" /></p>
<input type="hidden" name="url_title" id="url_title" value="{url_title}" maxlength="75" size="50" />
<input type="hidden" name="allow_comments" value="y" />
<input type="hidden" name="relation_lovforslag" value="<?php echo $entry_id; ?>" />
<input type="hidden" name="status" value="Closed" />
{field:wygwam_basic}
<input type="submit" name="submit" value="GEM KLADDE" class="form-submit" /></p>
{/exp:channel:form}This is for creating a related entry to the main channel entry. The field relation_lovforslag is for that purpose and it just sends the entry_id of the main entry. However, this doesn’t work anymore and I wonder what the proper syntax is for 2.7?